This needs to be fixed, as soon as I got in the area, I got the notification that it was active when it was not. This needs to fixed or some sort of compensation!
While this is indeed a bug, it is very minor, and possibly indicates that a Dynamic Encounter became active in another instance at the location. I occasionally see it while waiting for one to start at the beach area outside Hightide Hollow in Stonefalls. Sometimes I get lucky and am able to port into this active-DE instance via guild roster travel to player.